Strips of metal for girderlike constructional elements



Feb. 21, 1961 F. GREBNER 2,972,213

STRIPS OF METAL FOR GIRDERLIKE CONSTRUCTIONAL ELEMENTS Filed 001;. 16, 1957 2 Sheets-Sheet 1 (N VEN TOR: :FRITZ. GaEfin/an Q By 2,972,213 STRIPS OF METAL FOR GIRDERLIKE CONSTRUCTIONAL ELEMENTS Filed Oct. 16. 1957' F. GREBNER Feb. 21, 1961 2 Sheets-Sheet 2 IN VE N TOR FRITZ flEbA/ER ME T United Statesice STRIPS OF METAL FOR GIRDERLIKE CO1 STRUCTIONAL ELEMENTS Fritz Grebner, 70 Annabergstrasse, Mainz (Rhine), Germany This invention relates to strips of metal which are incised or slotted in such a way as to be capable of being expanded to form girder-like constructional elements of the type having an upper boom and two lower booms connected thereto by braces integral with the booms. For this purpose, the incisions or slots extend from points near, and substantially equidistantly spaced from, the center line of the strip to near a longitudinal edge of the strip.

Among the considerations which arise in the use of such strips are that the incisions or slots should be so disposed that: the strips can be easily expanded to form the girderlike member; the number of braces formed thereby should be a maximum so that the expanded girder may be sufficiently rigid to be self-supporting and carry light loads without the use of separate strengthening means; there should be adequate space available between the braces for accommodating longitudinal reinforcement means to adapt the girder for higher loads. 1

It is with such considerations in mind that the present invention has been developed.

According to the invention, a strip of metal is formed with two series of longitudinally extending incisions, one on each side of the center line of the strip and each series consisting of laterally spaced, longitudinally overlapping incisions, each incision comprising three substantially parallel rectilinear portions spaced at increasing distances fromthe center line and extending substantially parallel thereto, and oblique connecting portions between adjacent rectilinear portions, each rectilinear portion of each incision overlapping a rectilinear portion of two other incisions in the same series.

A strip having those characteristics meets the considerations mentioned above. in particular, it has been found that for a given depth of girder-like member to be formed there are more braces per unit length of the member than has hitherto been possible to obtain, without the need for reducing the width of the braces or increasing the width of the metal strip.

In expanding the strip to form the girder-like member it is preferred to bend the metal to as small a degree as possible and it is particularly desired to avoid bends of more than 90 in the braces because they would constitute points of weakness in the expanded member. The incisions on opposite sides of the center line are therefore preferably formed to extend from near the center line to near a longitudinal edge of the strip in opposite directions lengthwise of the strip. it is then possible to expand the strip to form a lattice-type girder in which the braces slope oppositely and are bent through only an acute angle at their ends and the process of expanding the strip is also considerably simplified thereby.

The strip of metal, and consequently the girder expanded therefrom, may have its stiffness increased at various points by means of stamped deformations which are preferably formed simultaneously with the incising or slotting step. For example the ribbons of metal which form the braces may be of approximately semi-cylindrical channel section throughout their lengths. Similarly, an axial portion of the strip which forms the upper boom of the girder may be longitudinally corrugated;

The invention also extends to the girder-like members which can be formed from such metal strips and to structural members incorporating the girder-like members, particularly reinforced-concrete members for forming floors or ceilings, the girders being primarily intended as reinforcement for the concrete.

In order that the invention may be clearly understood, an example of it will now be described with reference to the accompanying drawings in which:

Figure l is a fragmentary plan View of a strip of metal according to the invention,

Figure 2 is an enlarged fragmentary sectional elevation along the line 11-11 in Figure 1,

Figure 3 is a fragmentary view showing a detail of the girder of Fig. 4,

Figure 4 is a fragmentary perspective view of a girder expanded from a strip such as that in Figure 1 and embedded in a concrete block,

Figure 5 is a part-sectional end elevation of the girder with its lower booms embedded in concrete, and

.Figure 6 is a part-sectional enlarged fragmentary perspective view of the girder.

Referring to Figures 1 and 2, the metal strip 1 is provided with a series of stamped overlapping incisions 2 and 3, respectively, on each side of the centerline, each incision extending from near the center line to near a longitudinal edge of the strip to leave two unbroken longitudinal marginal portions 16 and an unbroken axial portion 4 lying between the two series of incisions.

Each of the incisions 2, 3 comprises three substantially parallel rectilinear portions 17 spaced at increasing distances from the center line and substantially parallel thereto. The portions 17 of each incision are connected by oblique portions 18.

. It will be noted that'each rectilinear portion 17 of each incision overlaps a rectilinear portion of two other incisions in the same series, that the incisions 2 extend towards'the marginal portion 16 in a direction lengthwise of thestrip'l opposite to that of the incisions 3 and that the incisions 2 are ofiset in relation to the incisions 3. Further, the incisions are arranged relatively to each other lengthwise of the strip so that the spacing of juxtaposed oblique portions 18 in a series is larger than the spacing of overlapping rectilinear portions 17 of successive incisions.

The overlapping parts of successive incisions in each series define between them a cranked ribbon of metal 19 which has its stiffness increased by a deformation in the form of a stamped longitudinal corrugation 6 which widens in the vicinity of the oblique portions 13 of the incisions.

Also for stiffening purposes, the axial portion 4 of the strip has stamped in it a corrugation 5 whilst near one end 8 of each ribbon 19 of metal there is provided a lobe-shaped corrugation 9 which is spaced from the ribbon 19 and which opens into the axial corrugation 5, the corrugation 9 diverging in width and depth towards the center line of the strip.

A corrugation similar to the one designated 9 could be provided adjacent the marginal portions 16 of the strip near the other end of each ribbon 19.

The strip of metal described above is of indefinite length and the pattern of incisions and deformations in the fragment illustrated in Figure l is repeated in either side of it.

.To expand the metal strip only one operation is necessary. Either the axial portion 4 is lifted from out of the plane of the marginal portions 16 whilst the latter are allowed to or assisted to move longitudinally relatively to one another, or theimarginal portions 16 are dislevel above the marginal portions. While doing so, the

cranked ribbons 19 of metal become bent transversely at their ends and the Whole can form a girder-like member as shown in Figures 3 to 5 having an upper boom 4 constituted by the axial portion 4 of the strip in Figure 1, two substantially coplanar booms 16 constituted by the marginal portions 16 of the strip in Figure 1 and two series of connecting braces 19 constituted by the cranked ribbons 19 of the strip in Figure l.

The girder as illustrated is of the lattice type and the braces 19 slope oppositely on either side, forming an angle of about 45 with the booms 16.

As shown in Figure 5, adequate space is available between the series of braces for accommodating longitudinal reinforcing rods 7 for the girder. The lower booms 16 have been stiffened by being deformed into channels 20, this being preferably done before the girder is expanded.

In Figure 6, a wooden spacer block 11 has been inserted in the channels 20 of the lower booms to secure the girder against collapsing under load, the spacer being held in the channels by pins 13. Pronged supports 14 "for'the rods 7 (Figure 5) are driven into the spacer 11 at intervals along its length. Instead of the spacer 11, clips or ties, 15 may be provided, as shown in dotted lines. The clips can have prongs bent out of them for holding the reinforcing rods 7.

The girder as described above, with or without the bars 7, spacer 11, or clips or ties 15, is particularly suitable as reinforcement for concrete structural members,

the entire girder being encased in the concrete (as shown in Fig. 4 in'dotted lines) or the upper boom 4 and upper parts of the braces '19 projecting therefrom (as shown in dotted lines in Fig. 5).

If it is desired to form girders which are deeper than that shown in Figure 3, that is to say if the braces 19 are to be longer, then the rectilinear portions 17 of the in cisions 2 and 3 in Figure 1 can be madecorrespondingly longer. Often, however, it is desired that the spacing of the lower booms of the girder be correspondingly in- ;creased. The invention permits this to be done without having to redesign the metal strip 1 simply by usinga Wider strip and adding a further oblique portion 18 and til 7 rectilinear portion 17 toeach incision. Each ribbon of metal bounded thereby would then form a brace which is cranked in two places.

What I claim is:

1. A self-supporting girder of an integral expanded sheet metal strip comprising a center boom, a pair of coplanar booms in a planeparallel to and spaced from the center boom, the coplanar booms being substantially symmetrically arranged at each side of the center boom, two series of braces integral with the booms and the braces in each series connecting the center boom to a respective one of the coplanarbooms, each brace having a cranked portion of greater width than the Width of the remainder of the brace intermediate the center boom and the coplanar booms, the braces in one series being'longitudinally staggered in'relation to the braces in the other series, joining portions of the same width as said braces for connecting the braces to the booms, said joining portions projecting from the booms so that each brace merges into a respective one of said joining portions adjacent the booms, and a laterally extending reinforcing bead in each of the joining portions adjacent the central boom and perpendicular thereto, the beads increasing in width and depth toward the center boom. 7

2. The self-supporting girder of claim 1, wherein the braces have a shaped cross section to increase their rigidity.

3. The self-supporting girder of claim 1, wherein the booms have a concave, shaped cross section to increase their rigidity.

4. The self-supporting girder of claim 3, wherein said reinforcing beads are lobe-shaped corrugations having a cavity in communication with the concave, section of the shaped boom adjacent thereto.

References Cited in the file of this patent UNITED STATES PATENTS 

